The present invention relates to an image-taking apparatus which allows image taking while a user observes an object image taken by an image-pickup device and displayed on a monitor, and a control method of the image-taking apparatus.
In an image-taking apparatus such as a single-lens reflex digital camera, part of light from an image-taking lens is reflected by a main mirror (an optical path splitting system) formed of a half mirror and is directed to a viewfinder optical system to allow a user to optically observe a subject (an object). The remaining light transmitted through the half mirror is then reflected by a sub mirror disposed at the back of the half mirror and is directed to a focus detection unit. The focus detection unit detects the focus state of the image-taking lens with a focus detection method such as a phase difference detection method. Based on the detection result, auto-focus (AF) operation is performed for driving a focus lens to an in-focus position.
In another proposed camera, in addition to or instead of the object observation through a viewfinder optical system, light transmitted through a half mirror is then directed to an image-pickup device to display an object image with an electronic viewfinder, while the remaining light reflected by the half mirror is then directed to a focus detection unit to perform AF operation (see Japanese Patent Laid-Open No. 2002-6208 and Japanese Patent Laid-Open No. 2004-264832). In such a camera, the half mirror is retracted from an image-taking optical path when a particularly high-definition still image is taken for recording.
When an object image is displayed with the electronic viewfinder (hereinafter referred to as “during the use of the electronic viewfinder”), the half mirror is put in the image-taking optical path and the optical path length is changed by the thickness of the half mirror as compared with the case where the half mirror is retracted from the image-taking optical path. Thus, the camera may not be focused on the image-pickup device through auto-focus operation based on the focus detection result when the half mirror is put in the image-taking optical path (during the use of the electronic viewfinder). In other words, a blurred image may be displayed in the electronic viewfinder.
To address this, in each of image-taking apparatuses disclosed in Japanese Patent Laid-Open No. 2002-6208 and Japanese Patent Laid-Open No. 2004-264832, the focus detection result is corrected by an amount corresponding to a change in optical path length due to the placement of the half mirror to achieve focus on the image-pickup device during the use of the electronic viewfinder.
In the image-taking apparat uses disclosed in Japanese Patent Laid-Open No. 2002-6208and Japanese Patent Laid-Open No. 2004-264832 in which auto-focus operation is performed to focus the camera on the image-pickup device during the use of the electronic viewfinder, conversely, the camera is not focused on the image-pickup device during image taking when the half mirror is retracted from the image-taking optical path. It is thus necessary to correct focus again by an amount corresponding to a change in optical path length due to the retraction of the half mirror during the image taking.
Focus correction is performed by driving a focusing lens of an image-taking lens. Particularly, in an image-taking lens such as a wide-angle image-taking lens which changes slightly its focus state relative to a moving amount of a focusing lens, the focus correction requires a large amount of driving of the focusing lens. In this case, there is a problem of a long time taken to make the transition from the operation of the electronic viewfinder to the ready state of image-taking operation, that is, a large time lag.